A known and promising technique for measuring molecular pollutants is laser spectroscopy. The technique, which uses a tunable and narrow linewidth laser light source, offers sensitive and selective detection of trace gases in the infrared (IR) spectral region.
Laser spectrometers use radiation passing through a volume of gas to detect a trace gas. As the radiation passes through the gas, some of its energy is absorbed by the gas at certain wavelengths. The range of wavelengths at which a trace gas exhibits characteristic absorption depends on the properties of the trace gas. For example, methane (CH4) strongly absorbs wavelengths of about 3.2 μm to about 3.5 μm, while carbon monoxide absorbs wavelengths from about 4.2 μm to about 4.5 μm. The level of energy absorption at the absorption wavelengths may be used to determine the concentration of a trace gas.
Recent developments in IR laser light sources radiating in the 3 μm to 10 μm wavelength range show great promise as nearly all molecules of trace gasses have characteristic absorption bands within this region.
Laser spectrometers may be used to detect a plethora of gasses including hydrocarbons, water vapor, and even calcium fluoride. Laser spectrometers are conventionally used in wastewater treatment facilities, refineries, gas turbines, chemical plants, mines, gas distribution lines, and other locations where flammable or combustible gasses may exist, as well as in atmospheric research.
However, current solutions have many shortcomings. Conventional laser spectrometers often use, for example, Quantum cascade (QC) lasers, which suffer from low conversion efficiency (and, thus, have high power consumption) and require heavy and expensive cooling mechanisms. Furthermore, commercial laser spectrometers that use lower-power consuming diode lasers often operate at near-IR wavelength ranges, where trace gas molecules may exhibit lower absorbance as compared to the IR range. Additionally, conventional solutions employ complex closed optical chambers (e.g., closed gas cells) with sophisticated mechanisms that sample and drive ambient air into the chamber while maintaining the chamber at nearly constant temperature and pressure, which may be below ambient temperature and pressure. This adds further complexity, size, and weight to the laser spectrometer, which drive up its power usage and cost.
Thus, what is desired is a low-cost, low-power, light-weight, portable, laser spectrometer for detecting and/or measuring the concentration of trace gases, and a method of using the same to detect trace gases.